The relationship between vesicular-arbuscular mycorrhiza and lime: Associated effects on the growth and nutrition of brachiaria grass (Brachiaria decumbens)

Abstract

We studied the effects of limining on growth and nutrient concentrations of Brachiaria decumbens inoculated with five vesicular-arbuscular mycorrhizal (VAM) fungal assemblages which orginated from soils with different acidity. Liming increased plant growth when applied at rates up to 3 g kg-1 soil and depressed growth at higher rates. Mycorrhizal plants grew better than non-mycorrhizal ones in unlimed soil and also liming rates of 4.5 and 6.0 g kg-1 soil. The growth amelioration effects of VAM in highly acid or over-limed soils were related to nutrient uptake. VAM fungi isolated from an acidic soil exhibited a high symbiotic effectiveness and were better adapted to unlimed soil than those that originated from non-acidic soils. VAM root colonization, 90 days after planting, was little affected by liming. Fungal spore production and species compositions were highly affected by liming. A mixture of Glomus diaphanum and Glomus occultum predominated in unlimed soils inoculated with VAM assemblages isolated from non-acidic soils. In these fungal assemblages, an increased liming rate favored Glomus etunicatum over the other VAM fungi. Gigaspora margarita sporulated abundantly when introduced into unlimed soils, but rarely in limed soils. VAM appear to be crucial for the establishment of brachiaria pastures in the nutrient-deficient acidic soils of Central Brazil. It is suggested that liming may cause striking shifts in VAM populations which may, in turn, have a long-term impact on agricultural productivity in the tropics.